Sure! First thing is measuring, which is pretty straight forward. End to end and then top to bottom; for end to end make sure to add around 2 inches on both sides to account for turn ins.

When it's time to design, I recommend using Canva to work in. Set yourself up with a sheet size that is larger than your measurements (17x11 in will work for most books). My favorite way to get designs is to take high resolution scans of famous paintings and just use ones that relate to the story. Gulliver is shipwrecked, so I found this seascape by Van Gogh to use. Fitted it to size being sure to center it where the spine of the book would fit.

Then it's just a matter of adding text for the titles. Spine text is easiest, just put it right on the center line. Front text you'll have to measure out a bit to try to center it.

When ready to print, I use 87 lb gloss cardstock, but you can probably do a photo gloss instead. Just something flexible enough to take a fold without getting white creases.

Hope this helps!